Browsing by Subject "Acetylcholin"

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Exzitatorische Pharmakologie der retinalen Spreading Depression
(2010) Sieber, Michaela; Hanke, Wolfgang
The phenomenon of Spreading Depression (SD) is a suppression of neuronal activity, propagating wave-like in the grey matter. This results from a massive ion translocation where potassium ions pour into the cell and sodium-, chlorideand calcium ions pour out of the cell. At the same time there is also a slow negative potential shift up to 30mV. Spreading Depression also occurs in the retina, a part of the central nervous system and can easily be observed there with the naked eye. This dissertation describes the effects of excitatory pharmaceuticals on neuronal tissue, using retinal spreading depression as a model system. By applying different excitatory substances, a reduction of the velocity and an inhibitory effect on the conductivity of the membranes can be observed. In the case of nicotine this may be due to the desensitization of the nicotinic AChreceptors. For caffeine, cocaine, amphetamine and metylphenidate this effect may derive from the hyperpolarisation of the tissue through open cation channels. The latency, a parameter for the excitability of the tissue, increases with the application of any of the investigated substances. This is also caused by the desensitization of the nicotinic ACh-receptors or the hyperpolarisation of the tissue, respectively. A neuroprotective effect reducing excitotoxic cell death induced by activation of NMDA-receptors was successfully verified for all substances. In the case of nicotine, the α7- and α4β2-nACh-receptors are assumed to be involved. The basic mechanism however is still unknown. A possible explanation could be the reduced excitability of the tissue through desensitization of the nACh-receptors. In the case of the remaining substances, the abidance of transmitters in the synaptic cleft suggests a neuroprotective effect through hyperpolarisation. The resulting hyperpolarisation leads to a reduced excitability of the neuronal tissue and most likely prevents over-excitation.